Gas or vapor phase particle production is an important technique for producing engineered materials, especially nanomaterials. Specific characteristics of particles produced in gas or vapor phase synthesis reactions depend not only on the energy delivered to the reactive medium, but also on the conditioning of the reactive medium once the medium has left the reactor.
In a particle production reactor, basic product species are formed within extremely short time spans as the reactive medium cools following ejection from the energy delivery zone. During the time following ejection, further formation mechanisms determine the ultimate characteristics of the final product.
Chemical reactions such as nucleation and surface growth occur within precursor materials largely during energy delivery. However, these formation mechanisms continue to be active in the first short moments following ejection. More prevalent in the post-ejection time period are bulk formation mechanisms, such as coagulation and coalescence, which operate on already formed particles. Proper conditioning of the reactive medium following ejection from the energy delivery zone accounts for these and other formation mechanisms to control formation of a final product having desired characteristics.
In addition to particle formation, proper conditioning must account for post-formation processing of the product. Although particles, once formed, cool rapidly through radiative heat loss, the residual gas in which they are entrained after formation cools much more slowly, and especially so when confined. Confinement is necessary to some degree in any controlled-environment processing system, and economic concerns usually dictate relatively confining controlled environments because large environments cost more to build and maintain. Because supply systems require product sufficiently cool for handling, such systems must provide efficient mechanisms for cooling of the entire gas-particle product, yet also provide for efficient transport of the product to collection points within the system. They must also prevent agglomeration of the particles beyond a certain point or time period to ensure proper grain size in the final product.
Transport of particles within a gas stream relies on entrainment of the particle, which is largely a function of particle properties, including mass, temperature, density, and interparticle reactivity, as well as gas properties, including density, velocity, temperature, viscosity, and composite properties, such as particle-gas reactivity. Cooling of a gas by definition affects gas temperature, but also may easily lead to changes in other properties listed above, exclusive of mass. In view of this, balancing efficient cooling and transport of gas-particle product requires careful optimization of process parameters, which the present invention seeks to achieve.